This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Study Design -- Animals: approx. 6 week old CD rats (250 gm);n = 6 -- Test article: Dobutamine, 30 ug/kg/min IV infusion Quantitative endpoints- total cardiac volume;left, right, and septal wall thickness;EDV, ESV, ejection fraction, stroke volume, cardiac output, fractional shortening Imaging: All imaging will be performed on the 1st-generation micro-CT system at the Duke CIVM. We will acquire 12 points in the cardiac cycle for 6 animals at two different times separated by at least one week. Each session will include a baseline followed by a challenge with dobutamine. Chronology: 2 animals imaged/day X 3 days. Animals will be returned to their cages for one week to recover to a baseline physiology and the study will be repeated. Phantom Calibrations: We will validate the CT scanning protocol and analysis using a phantom with objects of accurately known volumes. A (static) phantom will be constructed with CT (Hounsfield) differences comparable to those of the animal (myocardium/blood pool). The volumes of the phantom objects will be know with accuracy of at least 1%. The phantom will be scanned with techniques that produce contrast to noise at least 2X better than that seen in the clinical (live animal) setting. We will digitally alter the image sets to produce images with contrast to noise @ 0.5X, 1.0 X and (original) 2.0 X the CNR. This will allow us to separate any sources of errors from scanning and segmentation from the biological variability we wish to measure. Analysis: Phantom data will analyzed with three independent approaches : --- Autosegmentation using Vitrea cardiac functional analysis --- Autosegmentation using the PSC browser --- Semiautomated segmentation using Image J In all cases, the error will be reported relative to the gold standard (static phantom). At this point we may choose one or both methods to apply to the biological test data.